Polycrystalline films of silicon (poly-Si) are used to fabricate MOS transistors for static random access memory (SRAM) and large area display driver applications. Large area displays with resolution above several million pixels will be needed for applications such as high resolution graphics, HDTV, etc. One of the most important areas of this technology is driver circuits. At the moment, the display drivers are fabricated in thin films of polycrystalline or amorphous silicon deposited on an insulating substrate like glass or quartz. Low temperature processing is desirable for display driver applications because then the films can be deposited on substrates which preclude high temperature processing. For SRAMS, the lower temperatures are needed to scale down the device and circuit dimensions. One of the major problems being faced by investigators in this area is that the silicon films deposited by a technique like chemical vapor deposition (CVD) are amorphous below deposition temperatures around 550.degree. C. In order to obtain good polycrystalline films of Si, the deposition has to be done above 600.degree. C. MOS transistors fabricated in amorphous films have very poor properties and hence limited use. Higher temperature processing is thus required to convert amorphous silicon films to polycrystalline. For these reasons, the processing temperatures are limited to above 600.degree. C. to obtain reasonable MOS transistor performance.
Even with poly-silicon films, most of the electrical and physical properties of the thin film transistors made using conventional processing are controlled by grain boundaries. Dopant segregation, carrier trapping, anomalous thermal oxidation, and enhanced dopant diffusion are some of the effects of the grain boundaries which severely limit the opportunity to exploit this technology. In order to minimize the impact of grain boundaries, the major requirement is larger grain size in the film, as well as fabrication steps with low temperatures and short times. These requirements have not been met by polycrystalline silicon thin films.